I think so. I admit I wasn't too sure about what was happening—this is half of a person, separated from their wife, and seeking her out for… some reason I couldn't quite identify? I think the lack of understanding adds to the dramatic tension for this premise though, so I as a reader was totally okay with not knowing, even though typically I ask "why?" In this case, I get the chilling feeling that maybe I don't want to know why. And I don't see that often at all. This is solid horror, I think.

Is the tone clinical enough?

It looks decent overall. Couple of places I'd have reworded for Oxford commas and adverb placement, like "connected to a total parenteral nutrients system, a blood transfusion station and a class-B amnestic station intravenously" could be "intravenously connected to a total parenteral nutrients system, a blood transfusion station, and a class-B amnestic station". Also, some spots of casual wording like "All personnel entering the containment cell have to wear bite suits." I'd just state "must wear [something more standard and professional than "bite suit"?]". Also, grammar hiccups like "Should any contact with SCP-XXXX is interrupted".

Maybe read through the text out loud to smooth out some of these? Your call though; I tend to be pretty picky with wording.

I admit I wasn't too sure about what was happening—this is half of a person, separated from their wife, and seeking her out for… some reason I couldn't quite identify?

The premise is that this guy has been living for a long time, outliving all of his wives and kids in the families he built throughout millenia. He dealt with it by pretending that his "family" is always there; by this time it's more of a concept. He said this during the interview:

I have spent so much time looking for her, losing her and finding her again… Each time she disappears below the ground, with our child later after that… she would show up somewhere else…

YOU MORTALS CAN'T UNDERSTAND—

So now that he has brain damage and lost his current family from the accident, he tries to fuse with women to create a family again. That's why he "gave birth" to some fetus stuff at the end — it symbolizes the longing for a forged idea of a family, of togetherness. Whether it's because he reunites with his current wife or it's because he becomes desperate, after having his chance taken away by the researcher, I'll leave it up to readers' interpretation.

If I could make the backstory more apparent, should I do it? Would it diminish this sense of dread originated from not-knowing like you said?

He dealt with it by pretending that his "family" is always there; by this time it's more of a concept. He said this during the interview:

Oh. I didn't really pick up on that, I thought he was trying to find the reincarnation of his first wife or something.

If I could make the backstory more apparent, should I do it?

Eh… if you simplify it a bit. I'm not sure about how well the "coping by pretending the family is always there" bit will come through, but I think the audience can quickly determine the guy's desire to have a family again. Just focus on that rather than the coping?

Would it diminish this sense of dread originated from not-knowing like you said?

Cleaning and maintenance are to be completed only after SCP-XXXX is injected with amnestic.

amnestic -> amnestics

SCP-XXXX is a 0.7m x 0.24m right half of a torso of a 40-year-old Caucasian man

But later, you say:

The loss of the left hemisphere severely impairs SCP-XXXX's language comprehension,

…which implies it has a head,, despite the torso not including the head.

SCP-XXXX rejects any foreign tissues on a cellular level, as replantation has been proven unsuccessful.

level, as -> level; due to this,

Without amnestic or other means of intervention1, SCP-XXXX will consolidate the host body for [DATA EXPUNGED].

I don't see why this is expunged. I feel like this could only be made stronger by describing why SCP-XXXX does what it does. Maybe even an opportunity to induce imagery.

SCP-XXXX was retrieved after a [REDACTED] accident occurred at ██:██, ██/██/20██, in ██████, United States. Initially, it was listed as one of the three casualties; the other two were identified as █████ ████████ and ███████ ████████, its wife and young daughter.

I don't see the point of this if you're just going to redact it. Again, I think it could be made stronger without the redaction.

The acquisition of CCTV footage within the ██:██ - ██:██ interval were authorized.

were -> was

YOU MORTALS CAN'T UNDERSTAND—

This just seems kind of cliche. I'd axe the "MORTALS" part

If you want to execute horror, you have to use the three parts of horror, Setup, Escalation, and the Twist.

Setup: I think your setup is where you're getting your skip wrong. By the time I come out of your setup, I should be feeling at least somewhat uneasy. Here are some problems I noted:

1). You don't really describe how SCP-XXXX integreates himself in much detail. This is a good place to amp up the body horror and give the reader a better mental image of your SCP.

2). The redactions above get in the way of telling how your SCP came to be; I find that the origin story of your SCP makes for good setup; you're missing out on it here.

Escalation: In my opinion, you rush too fast through your escalation. You need to pace it some more; maybe add some more tests.

In addition, your dialogue is just kind of dumped in one place. Adding more tests would help with this; try to scatter this dialogue over the course of several tests.

Twist: I feel like, if your setup and escalation were more effective, your twist would be more effective. I feel like the addenda might not be necessary; I'd axe them if I were you. Other than that, I really have no comment here.

You don't really describe how SCP-XXXX integreates himself in much detail. This is a good place to amp up the body horror and give the reader a better mental image of your SCP.

I delved into the details about how the man does his things in one of the test logs. Do you think I should move it to the description, or do you think I should expand on it?

I find that the origin story of your SCP makes for good setup

You mean how the guy was cut in half and lost his family, or why he fuses with other people? If it's the latter then I've already tried to construe the dialogue so as to give readers hints about it.

If it's the former though, it's nothing much: guy and family driving on the highway and got hit by a truck. Guy got half of his body cut off upon collision, while wife and daughter died from the impact to the ground. Some dude from Reddit told me that veiling the origin gives more mystery to the SCP.

Adding more tests would help with this; try to scatter this dialogue over the course of several tests.

Ish, this is where my inexperience stands out: I don't know what to write other than what I already wrote. I think that the interview is about getting to know the motive of the character, and that's it. Scattering such a short conversation would feel forced.

What if I put another interview when the guy fuses with the first female subject? He will beat around the bush, given his impaired language skill, then the researcher give up and wait for the next test.

The problem here is that I can't decide if there's anything to encourage SCP-XXXX to spill the beans other than getting him whole. Initially, I wanted to devise his fusing mechanisms like this: the more similar the subject is to his wife, the more SCP-XXXX is willing to integrate. But now that I've stated the dude just sees any female as his wife, that idea doesn't work anymore.

I feel like the addenda might not be necessary; I'd axe them if I were you

On the contrary, I feel they tie up the loose ends; they are the denouement. Though I can understand that if the components preceding them are unsatisfactory, they might seem unnecessary. I'll focus on polishing up the body.

Note: I correct the given mistake only once. If you do not use the metric system, I will only make a single comment about it, even if it appears again in the rest of the article. If the draft has many language problems, I will only correct the most glaring ones.

However, if the integration is not interrupted, the half of the body SCP-XXXX consolidates will remain functional up to a week; how the specimen preserves the body is unknown. After that, the corpse will starts decomposing and disconnected from SCP-XXXX

Try to avoid verbiage like 'after that' and 'repaired later'. Instead, say 'regenerate after a later stage' or the like.

All repairs are done with sinews of microscopic sizes.

Are performed?

which blocks the neurotransmiters

neurotransmitters*

At 20:11, in the morgue unit of [REDACTED] Hospital, SCP-XXXX regained consciousness. It merged with one of the coroners and attempted to exit the facility, before captured by Mobile Task Force Phi-9 ("Milk and Cream").

That was quick. Wouldn't local police get to it first?

SCP-XXXX: Really? Like I said, I totally feel fine and— Oh, here's my wife. Why didn't tell me that you put my wife right next to me from the beginning?

This doesn't sound very natural. Try to say what the SCP says out loud, right now. Doesn't that feel a bit rehearsed? Why didn't he talk to her right away?

That kind of crazy, wacky TV show where you scare the crap out of people then surprise them with something nice, right?

Same here. This man is supposed to be traumatised, these sentences are way too long-winded and elaborate. Try to make it more natural without being too overdramatic.

It's okay, stick to the script! Where's the camera? Here? (SCP-XXXX looks at the surveillance camera in the corner of the containment cell.) Hey folks, you got me! You got an old man on his nerves! Hey Clarissa, nice job getting daddy stirred up! If this is how you want to get daddy to talk to you, fine, I'll start talking! I'll talk so much you won't be able to bring your friends over anymore!

See, this is better. Shorter, stilted sentences, giving off the air of denial. Throw a few pauses and quickening heartbeat/breathing in there.

SCP-XXXX: Find out what? About why I suddenly became… this?

This is acceptance already, way too quickly. I recommend making a timelapse or note that this is after multiple attempts where the SCP isn't comprehensible.

SCP-XXXX: Extreme? Does my loss mean nothing to you? Why don't you just, report to the police or the news or someone else? Are you gonna keep me here forever so that you can laugh at me?

Not laugh, I'd say something like 'perform your weird experiments on me?' or 'I'm not a test subject, I'm a patient!' And that he wants to see his wife and child, at least to say goodbye. Then you can have the doctor say that they're not sure if they can do that, but see what they can do. The doctor has to appeal to reason, calm him down before continuing the questioning.

Definitely better already, but try to work on your clinical tone in the description, and the dialogue in the audio log. Don't go too fast, ease the reader into the personality of the SCP and the doctor, give us a few more moments of normalcy after his condition settles in.